In recent years, print processing speed of image forming apparatuses has become high-speed, and there has been growing demand for a large amount of printing. In order to satisfy the demand, high-capacity paper feeders have been developed as an optional device for a standard paper-feeding cassette (usually, the cassette can store approximately 500 sheets of paper) of an image forming apparatus. In many cases, a high-capacity paper feeder is adapted so that a large number of papers of one kind are stored, and that shortage of papers in the paper-feeding cassette is replenished. Further, there has also been proposed an arrangement in which several kinds of papers are respectively stored in separate paper storing sections which are disposed one above the other (see, for example, Japanese Unexamined Patent Publication No. 193766/1993 (Tokukaihei 5-193766, published on Aug. 3, 1993)).
FIG. 8 schematically illustrates a paper feeder installed in an image forming apparatus as disclosed in the above publications and elsewhere. In the figure, an image forming apparatus 700 includes an image forming section 701 adopting the electrophotographic process, a paper-supply section 702 that supplies a paper to the image forming section 701, and a fixing section 703. The fixing section 703 is disposed in a midway of a transport path through which a paper with an image formed by the image forming section 701 is ejected out of the image forming apparatus 1.
The paper-supply section 702 includes paper-feeding cassettes 702a and 702b that respectively store different sizes of papers and are disposed one above the other. A paper is supplied from a selected upper or lowest cassette to the image forming section 701. Then, the image forming section 701 forms an image onto the paper. In the case where double-sided image formation is performed, the paper, after transiting the fixing section 703, is looped back to the image forming section 701 through a sub paper-transport path 704, with the paper turned upside down.
Further, in addition to the paper-supply section 702 installed in the image forming apparatus 700, a manual paper-supplying path 705 is provided that is for supplying a paper of arbitrary size to the image forming section 701 upon necessity. A manual paper-supply section (not illustrated) is disposed on part of the manual paper-supplying path 705 from which a paper enters, so that a manually supplied paper is transported to the image forming section 701.
The image forming apparatus 700 structured as described above is provided with an external paper feeder 706 as an optional device, in addition to the paper-supply section 702 installed in the image forming apparatus 700. The external paper feeder 706 is installed on the image forming apparatus 700 in such a manner that it is in communication with the manual paper-supplying path 705 of the manual paper-supply section. The external paper feeder 706 includes, for example, vertically disposed three paper storing sections 706a, 706b, 706c that have a higher capacity than the paper-supply section 702 of the image forming apparatus 700. A paper at the top of the papers stored in the paper storing sections 706a, 706b, 706c is transported first. The transported paper is guided to the manual paper-supplying path 705 and is transported into the image forming apparatus 700 therefrom.
The paper feeder 706, as illustrated in FIG. 8, that is disclosed in the above publications is structured in such a way that several kinds of papers are stored in separate paper storing sections 706a to 706c that are vertically disposed. As such, the paper feeder 706 includes transport paths each formed for each type of papers to be stored. Further, the transport paths merge at one place, from which a paper is supplied to the image forming apparatus. In such structure of the paper feeder 706, a plurality of curves are formed in the transport paths in the paper feeder 706, and the curves exist in a limited space. This often causes jam or skewed transport of a paper while the paper is being transported in the paper feeder 706.